The present invention is directed to novel isotropic aromatic polyesters, i.e. polyarylates.
Linear aromatic polyesters prepared from dicarboxylic acids, especially from aromatic dicarboxylic acids and bisphenols are well known for their suitability for molding, extrusion, casting, and film-forming applications. For example, U.S. Pat. No. 3,216,970 to Conix, discloses linear aromatic polyesters prepared from isophthalic acid, terephthalic acid, and a bisphenolic compound. Such high molecular weight compositions are known to be useful in the preparation of various films and fibers. Further, these compositions, when molded into useful articles using conventional techniques, provide properties superior to articles molded from other linear polyester compositions. For instance, aromatic polyesters are known to have a variety of useful properties, such as good tensile, impact, and bending strengths, high thermal deformation and thermal decomposition temperatures, resistance to UV irradiation and good electrical properties.
It is known to impart desired physical properties to polyarylate resins by the inclusion of additives. However, the inclusion of additives to polyarylate obviously increases the expense of such compositions above the polyarylate resin itself. Moreover, often while improving one physical property, the additives may degrade another property inherent in the polyarylate resin. Accordingly, it would be worthwhile to improve the inherent properties of the polyarylate without resorting to the excessive addition of modifying substances.
In forming polyarylates, in general, it is necessary to conduct the polymerization in two stages. In the first stage, a prepolymer is formed typically having an intrinsic viscosity of up to 0.3 dl/g. The prepolymer is formed by condensing the aromatic dicarboxylic acid components with the bisphenolic compound. In the second stage, polycondensation takes place resulting in an aromatic polyester having an I.V. of greater than 0.4 dl/g. While the two-step process has proven useful to yield acceptable polymeric materials, it would be worthwhile to prepare a polyarylate in one step providing polyesters of intrinsic viscosity of greater than 0.4 dl/g without resorting to the prepolymer/post polymerization two-stage process.
The primary objectives of the present invention are to produce a polyarylate having inherently improved properties and to form the aromatic polyesters in only one step and still provide the polyesters with sufficiently high molecular weight.